1. Field of the Invention
The present invention relates to a semiconductor device by which communication of data is performed wirelessly.
2. Description of the Related Art
In recent years, individual identification technology using wireless communication has been gathering attention. In particular, individual identification technology using RFID (radio frequency identification) tags as semiconductor devices by which exchange of data is performed by wireless communication has been gathering attention. RFID tags (hereinafter, simply called RFID) are also referred to as IC (integrated circuit) tags, IC chips, RF tags, wireless tags, and electronic tags. Individual identification technology using RFID has begun to be used in the production and management of individual objects, the identification of individual people, and the like.
RFID can be divided into two types, active RFID in which electromagnetic waves that include RFID information can be received and passive RFID that is driven using electric power of electromagnetic waves from an external source, depending on whether a power supply is built-in or whether a supply of power is received from an external source. In Patent Document Reference 1: Japanese Published Patent Application No. 2005-316724, there is a description related to active RFID. Furthermore, in Patent Document Reference 2: Japanese Translation of PCT International Application No. 2006-503376, there is a description related to passive RFID. Active RFID has a built-in power supply used for driving the RFID. Passive RFID has no built-in battery but power is generated using electric power of received electromagnetic waves.
In FIG. 21, a block diagram of a specific structure of active RFID is shown. In active RFID 300 in FIG. 21, communicated signals received by an antenna circuit 301 are input into a signal processing circuit 302. Commonly, processing of ASK modulation, PSK modulation, or the like is performed on a carrier wave of 13.56 MHz, 915 MHz, or the like, and the communicated signals are transmitted. In FIG. 21, an example of a structure of active RFID where the frequency of the communicated signals is 13.56 MHz is shown.
In the RFID 300, a standard clock signal for processing signals is needed, and, here, a carrier wave of 13.56 MHz is used as the clock. An amplifier 307 amplifies the 13.56 MHz carrier wave and supplies the 13.56 MHz carrier wave to a logic circuit 308 as a clock. In addition, a communicated signal modulated by ASK modulation or PSK modulation is demodulated by a demodulation circuit 306. After being demodulated, the signal is also transmitted to the logic circuit 308 and analyzed. The signal analyzed by the logic circuit 308 is transmitted to a memory controller circuit 309. Based on this signal, the memory controller circuit 309 controls a memory circuit 310, and data stored in the memory circuit 310 is retrieved and transmitted to a logic circuit 305. After the data is encoded by the logic circuit 305, the signal is amplified by an amplifier 304, and by this signal, modulation is applied to the signal by a modulating circuit 303. Here, in FIG. 21, power is supplied by a battery 261 through a power supply circuit 260. The power supply circuit 260 supplies electric power to the amplifier 307, the demodulation circuit 306, the logic circuit 308, the memory controller circuit 309, the memory circuit 310, the logic circuit 305, the amplifier 304, the modulation circuit 303, and the like. Active RFID operates in this way.
In FIG. 20, a block diagram of a specific configuration of a passive type of RFID is shown. In passive RFID 200 in FIG. 20, communicated signals received by an antenna circuit 201 are input into a signal processing circuit 202. Commonly, processing of ASK modulation, PSK modulation, or the like is performed on a carrier wave of 13.56 MHz, 915 MHz, or the like and the communicated signals are transmitted. In FIG. 20, an example of a structure of passive RFID where the frequency of the communicated signal is 13.56 MHz is shown.
In the RFID 200, a standard clock signal for processing signals is needed, and, here, a carrier wave of 13.56 MHz is used as the clock. An amplifier 207 amplifies the 13.56 MHz carrier wave and supplies the 13.56 MHz carrier wave to a logic circuit 208 as a clock. In addition, a communicated signal modulated by ASK modulation or PSK modulation is demodulated by a demodulation circuit 206. The demodulated signal is also transmitted to the logic circuit 208 and analyzed. The signal analyzed by the logic circuit 208 is transmitted to a memory controller circuit 209. Based on this signal, the memory controller circuit 209 controls a memory circuit 210, and data stored in the memory circuit 210 is retrieved and transmitted to a logic circuit 205. After the data is encoded by the logic circuit 205, the signal is amplified by the amplifier 204, and by this signal, modulation is applied to the carrier wave by a modulating circuit 203. Meanwhile, the communicated signals input into a rectifier circuit 220 are rectified and input into a power supply circuit 221. The power supply circuit 221 supplies electric power to the amplifier 207, the demodulation circuit 206, the logic circuit 208, the memory controller circuit 209, the memory circuit 210, the logic circuit 205, the amplifier 204, the modulation circuit 203, and the like. Passive RFID operates in this way.
In active RFID like that shown in FIG. 21, in response to strength settings of signals needed for transmission and reception of information of individual objects, a battery is drained over time, and, finally, electric power needed for communication of information for individual objects comes to be unable to be generated. For this reason, for continued use of a semiconductor device that includes active RFID, operations for checking the remaining capacity of a battery and changing the battery are needed.
Meanwhile, in passive RFID like that shown in FIG. 20, because power for driving is produced using electric power of electromagnetic waves from an external source, securing electric power for transmission of information long distances is difficult and realizing stable communication of information long distances is problematic. For this reason, in passive RFID, the usage range is limited to usage for short-distance communication in which the supply of electric power of electromagnetic waves supplied from an external source comes to be enough.